Electron discharge device



May 14, 1963 F. L. WASHBURN, JR 3,089,975

ELECTRON DISCHARGE DEVICE Filed-Nov. 21, 1961 1 46 -INVENTOR FrederickL. Woshburmdr ATTORNEY 3,089,975 Patented May 14, 1963 3,039,975ELECTRON DISCHARGE DEVICE Frederick L. Washburn, in, Round Bay, SevernaPark, Mi, assignor to Westinghouse Electric Corporation, EastPittsburgh, Pa, a corporation of Pennsylvania Fiied Nov. 21, 1961, Ser.No. 153,995 6 Claims. ((31. SIS-3.6)

The present invention relates generally to electron discharge devices,and more particularly to slow-wave propagating structures for use indevices such as traveling-wave tubes.

Traveling-wave tubes comprise generally an elongated envelope with anelectron beam producing means. disposed at one end thereof for theproduction and projection of an electron beam through the envelope. Aslow-wave propagating means coaxially mounted within the envelopefunctions to propagate electromagnetic energy along the length of theenvelope in an interacting relationship with the electron beam. Anelectron collector assembly is disposed at the opposite end of theenvelope for collecting the electron beam.

It has been shown that a non-contacting cross-wound structure having twohelices which are oppositely wound and interposed has a mode whichpossesses higher impedance in the fundamental and lower impedance in thespatial harmonic than a single helix (Chodorow and Chu, Cross-Wound TwinHelices for Traveling-Wave Tubes, Journal of Applied Physics, volume 26,pages 33-43; January 1955). It has also been shown that such acrosswound structure has less velocity dispersion than the usualring-and-bar structure which is in general present-day use. However,such a non-contacting structure in which the two helices have the sameradius and longitudinal axis and which is suitable for high frequencyoperation has not lent itself to being readily manufactured. Those thathave been made have had large areas of contact between the helices witha resulting degradation in the slowing efiect of the structure. It isfor this reason that the prior devices have generally utilizedstructures of the ring-and-bar type.

It is, therefore, an object of this invention to provide an improvedelectron discharge device.

A further object of this invention is to provide an improved slow-wavepropagating means for use in electron discharge devices.

Another object is to provide a slow-wave propagating structure of thecross-wound helices which are non-contacting in the usual sense.

A further object of this invention is to provide a slowwave propagatingstructure comprising two cross-wound helices having only a small contactarea.

A still further object is the provision of a slow-wave propagatingstructure which consists of two helices for med in opposite senses andwhich are non-circular in crosssectional configuration.

Stated briefly, this invention is directed to a traveling- Wave tubewhich utilizes two helical members of slightly non-circularconfiguration which, when fitted together, form a substantially circulartunnel through which the electron beam passes. The slightly non-circularconfiguration permits the two helices to be fitted together in aninterposed manner and yet does not allow the helices to contact oneanother in the normal sense of the term.

Further objects and advantages of the invention will become apparent asthe following description proceeds and features of novelty whichcharacterize the invention will be pointed out in particularity in theclaims annexed to and forming a part of this specification.

For a better understanding of the invention, reference may be had to theaccompanying drawings in which:

FIGURE 1 is an elevational view partially in section, of atraveling-wave tube embodying the present invention;

FIG. 2 is a schematic representation of two helices wound in oppositesenses or in a cross-wound configuration which do not embody the presentinvention;

FIG. 3 is an end view of the two helices of FIG. 1 showing thenon-circular configuration;

FIG. 4 is an exploded view of the two helices of FIG. 1 which are woundin opposite senses in accordance with the present invention;

FIG. 5 is a cross-sectional view taken along line VV of FIG. 1 andshowing two non-circular helices assembled in accordance with thepresent invention; and

FIG. 6 is a modification of FIG. 5' showing the preferred embodiment ofthe present invention.

With specific reference to FIG. 1, there is shown an electron dischargedevice of the traveling-wave tube type comprising an envelope 11comprising a central tubular portion 13, which may be made of a suitablematerial such as glass, and two enlarged end portions 15 and 17, whichare of a suitable material such as copper, and which are connected andsealed to the glass tube 13'. An electron beam source, indicatedgenerally by the reference character 2, is disposed at one end of theenvelope 11 within the bulb portion 15. This beam source 2 comprises anelectron emissive cathode 19, a focusing electrode 21, and anaccelerating electrode 23. These elements are connected to suitablesources of voltage, which have not been shown, and collectively act toproduce and direct a beam of electrons centrally along the axial lengthof the envelope 11 to the opposite end of the envelope. An electroncollector 25 is positioned at the opposite end of the envelope 11 withinthe bulb portion 17 and serves to collect the electrons of the beamafter they have passed through the tubular portion 13.

A slow-wave propagating means 27 .is positioned intermediate theelectron beam source 2 and collector 25. This propagating means 27functions to propagate electromagnetic energy along the length of thetubular portion 13 in an interacting relationship with a major portionof the outer edge electrons of the electron beam. The propagating meansin the present instance is two separate helices 37 and 41 ofelectrically conducting material formed into a cross-wound configurationas will be more fully explained later.

Electromagnetic energy is supplied to the slow-wave propagating means 27by means of a waveguide 29 which is positioned near the enlarged portion15 in a manner well known in the art. Similarly, a second wave-guidestructure 31 is provided near the enlarged portion 17 for the removal ofelectromagnetic energy from the slow-wave propagating means 27.

The propagating means 27 is supported within the envelope 11 by means ofa plurality of supporting rods 33 which are disposed along the axiallength of the envelope for substantially the entire length of thepropagating means 27. The support rods 33 are preferably made of 'asuitable heat conducting, electrical insulating material such as aluminaor beryllia. In the present example, four support rods are utilized.

In order to prevent the electron beam from spreading to such an extentthat it would be intercepted by propagating means 27, it is necessary toprovide some form of focusing. Focusing in the present instance isprovided by producing a magnetic field axially along the envelope 1 1 bythe utilization of a long annular solenoid 35 which surrounds theenvelope 11 for substantially the entire length of the propagating means27. To simplify the 3 present drawing and description, the solenoid 35is only schematically illustrated and its source of energization is notshown.

Referring now to FIG. 2,there are shown two circular helices 52. and 54which are wound in opposite senses and :which do not embody the presentinvention. Crosshatched area A indicates the amount of contact areawhich is present at each cross-over of the two helices 52 and 54. Withthis type structure, the currents of the electro-magnetic energy whichis being propagated along helices 52 and 54 tend to take the shorterpath to the next cross-over as is represented by line B rather than takethe longer preferred path which is represented by line C. This taking ofthe shorter path lessens the slowing efiect and hence reduces theeffectiveness of the propagation structure. As is readily apparent, asthe pitch of helices is lessened, the area of contact is increased andthe short path represented by line 3 becomes even shorter relative tothe preferred path (line C) with a resulting increase in the tendencyfor the currents to take the shorter path.

With reference now to FIGS. 3 through 5, there are shown enlarged viewsof the slow-wave propagating means of FIG. 1 in accordance with thepresent invention. A first helical member 37 of conducting material isformed substantially circular in cross-sectional area but is madeslightly non-circular insofar as it includes an offset portion 39. Theportion 39 should be offset only slightly more than the thickness of thematerial constituting the helical member. In a like manner, a secondhelical member 41 of conducting material and having the same basicradius as the first helix 37 is provided with an offset portion 43. Theoffset portion 39 of member 37 is shown to be on the left while theoffset portion 43 of member 41 is shown to be on the right. As is bestshown in FIG. 4, member 37 shown to be wound in the left-hand orcounterclockwise sense while member 41 is shown to be wound in theright-hand or clockwise sense. Each of the helical members 37 and 41 areformed so as to have the same basic radius and the same pitch. After thehelical members 37 and 41 have been so formed, they are interposed orpositioned together in such a maner so as to be coaxial. As Well asbeing coaxial, the helical members are arranged so that a circularportion 38 of member 37 corresponds angularly and longitudinally withthe offset portion 43 of helical member 41 and in a like manner thecircular portion 42 directly opposite offset portion 43 of member 41 isin direct angular and longitudinal alignment with the offset portion 39of helicalmernber 37. By this arrangement, as can best be seen in FIG.5, a substantially circular tubular member or slow-wave propagatingmeans is achieved. The two helical members which together constitute theslow-wave propagating means 27 may now be positioned within the envelope11 and supported therein by the electrically insulating supportingmembers 33. In the present example, four such insulating members 33 areused to support the slow-wave propagating means 27 within the envelope11.

Because non-contacting cross-wound helices can potentially operate in apush-pull mode giving rise to feedback and/or backward waveoscillations, some type of mode suppression is often desirable. FIG. 6illustrates the present invention in its preferred form. The embodimentshown in FIG. 6 is the same as that shown in the earlier figures (FIGS.25) with the addition of small tabs or points 45 which are formed oneach of the offset portions 43 and 39 (although they may be formed onthe circular portions 42 and 38 with equal advantage). These tabs 45 ofsuch a size as to provide substantially a point contact between the twohelical members 37 and 41. While it is true that there is some contactbetween the two members in this instance, this contact is of a verysmall area and does not make the helical members contacting in the usualsense of the word. The amount of actual contact between the helicalmembers 37 and 41 is insufficient to permit the currents flowing in onehelix to trnsfer to the other but yet is sufiicient to suppress apush-pull mode of operation.

The helical members 37 and 41 constituting the slowwave propagatingmeans 27 are made for a suitable conducting material, for examplemolybdenum, and may be of wire, tape, or of tubular configuration. Ifthe tubular configuration is used, the slow-wave propagating means 27possesses the additional advantage that it may be liquid cooled. Thiscooling method is illustrated in FIG. 1 in which the two helical membersare shown to be connected on one end to an input manifold 47 to whichfluid is supplied by means of a conduit 48. At the other end of theslow-wave propagating means 27, the two helical members are connected toa manifold 49 which in turn is connected to a conduit 50 which removesthe fluid from the slow-wave propagating structure. The conduits 48 and50 are in turn connected to a fluid circulating means, for example, apump, which has not been shown.

While there have been shown and described what are at present consideredto be the preferred embodiments of the invention, modifications theretowill readily occur to those skilled in the art.

For example, the helices could each be of bifilar or multifilarconfiguration rather than the two simple helices shown. It is notdesired, therefore, that the invention be limited to specificarrangements shown and described and it is intended to cover in theappended claims all such modifications as fall within the true spiritand scope of the invention.

I claim as my invention:

1. A traveling wave tube comprising an envelope, means disposed at oneend of said envelope for the production and projection of an electronbeam along the axial length of said envelope, means disposed at theother end of said envelope for the collection of said electron beams,slow-wave propagating means disposed within said envelope substantiallycoaxial and in an interacting relationship with said electron beam, saidslow-wave propagating means comprising first and second helical membersof conducting material wound in opposite directions with respect to eachother and having the same basic radius and longitudinal axis, each ofsaid helical members having a series of outwardly extending offsetportions at alternate points where the two helical members cross oneanother.

2. An electron discharge device comprising an envelope, means disposedat one end of said envelope for the production and projection of anelectron beam through said envelope, means disposed at the opposite endof said envelope for collecting said electron beams, slow-wavepropagating means disposed within said envelope in an interactingrelationship with said electron beam, said slowwave propagating meanscomprising a first electrically conducting helix formed in a first senseand a second electrically conducting helix interposed with said firsthelix and formed in the opposite sense, each of said helices having thesame basic radius and longitudinal axis and each having an offsetportion at alternate points of cross over to prevent contact of the twohelices.

3. An electron discharge device comprising an envelope, means disposedat one end of said envelope for the production and projection of anelectron beam through said envelope, means disposed at the opposite endof said envelope for collecting said electron beams, slow-wavepropagating means disposed within said envelope in an ration atalternate points of crossover of said members to preclude substantialcontact between said helical members.

4. An electron discharge device comprising an envelope, means disposedat one end of said envelope for the production and projection of anelectron beam through said envelope, means disposed at the opposite endof said envelope for collecting said electron beam, slow-Wavepropagating means disposed within said envelope in an interactingrelationship with said electron beam, said slowwave propagating meanscomprising a first helical member for-med in a first sense and a secondhelical member formed in the opposite sense, said helical membens havingthe same basic radius and same longitudinal axis to provide asubstantially cylindrical tube in cross section, each of said helicalmembers having an offset portion at alternate points Where said helicalmembers cross, said helical members being of tubular configuration andmeans for forcing a cooling fluid through said tubular members.

5. An electron discharge device comprising an envelope, means disposedat one end of said envelope for the production and projection of anelectron beam through said envelope, means disposed at the opposite endof said envelope for collecting said electron beam, slow-wavepropagating means disposed with said envelope in an interactingrelationship With said electron beam, said slow- Wave propagating meanscomprising first and second helical members formed in opposite sensesand having the same basic radius and longitudinal axis, each of saidhelical members having offset portions at alternate points 6 ofcrossover of said helical members, and tab members provided on one ofsaid helical members at each crossover point to provide a point contactbetween said members.

6. An electron discharge device comprising an envelope, means disposedat one end of said envelope for the production and projection of anelectron beam through said envelope, means disposed at the other end ofsaid envelope for collecting said electron "beam, slow-Wave propagatingmeans disposed Within said envelope in an interacting relationship withsaid electron beam, said slow-Wave propagating means comprising firstand second helical members formed in opposite senses and having the samebasic radius and longitudinal axis, each of said helical members havinga non-circular portion at alternate points of crossover of said helicalmembers for the prevention of substantial contact between said helicalmembers, and means disposed on one of said helical membars to provide anarea of contact of insufficient area to permit substantial transfer ofenergy from one helical member to the other.

References tilted in the file of this patent UNITED STATES PATENTS2,997,618 Watkins Aug. 22, 1961 FOREIGN PATENTS 1,071,858 France Sept.6, 1954

1. A TRAVELING WAVE TUBE COMPRISING AN ENVELOPE, MEANS DISPOSED AT ONEEND OF SAID ENVELOPE FOR THE PRODUCTION AND PROJECTION OF AN ELECTRONBEAM ALONG THE AXIAL LENGTH OF SAID ENVELOPE, MEANS DISPOSED AT THEOTHER END OF SAID ENVELOPE FOR THE COLLECTION OF SAID ELECTRON BEANS,SLOW-WAVE PROPAGATING MEANS DISPOSED WITHIN SAID ENVELOPE SUBSTANTIALLYCOAXIAL AND IN AN INTERACTING RELATIONSHIP WITH SAID ELECTRON BEAM, SAIDSLOW-WAVE PROPAGATING MEANS COMPRISING FIRST AND SECOND HELICAL MEMBERSOF CONDUCTING MATERIAL WOUND IN OPPOSITE DIRECTIONS WITH RESPECT TO EACHOTHER AND HAVING THE SAME BASIC RADIUS AND LONGITUDINAL AXIS, EACH OFSAID HELICAL MEMBERS HAVING A SERIES OF OUTWARDLY EXTENDING OFFSETPORTIONS AT ALTERNATE POINTS WHERE THE TWO HELICAL MEMBERS CROSS ONEANOTHER.